A hydrogen-producing fuel processing assembly is an assembly of one or more devices or components that includes a fuel processor with a hydrogen-producing region that is adapted to convert one or more feedstocks into a product stream containing hydrogen gas as a majority component. In operation, the hydrogen-producing region is typically operated at an elevated temperature and pressure and contains a suitable catalyst to produce at least hydrogen gas from the feedstock(s) delivered thereto. The composition, flow rate, and properties of the feedstock(s) delivered to the hydrogen-producing region may affect the performance of the hydrogen-generation assembly.
The produced hydrogen gas may be used in a variety of applications. One such application is energy production, such as in electrochemical fuel cells. An electrochemical fuel cell is a device that converts a fuel and an oxidant to electricity, a reaction product, and heat. For example, fuel cells may convert hydrogen and oxygen gases into water and electricity. In such fuel cells, the hydrogen gas is the fuel, the oxygen gas is the oxidant, and the water is the reaction product. Fuel cells are typically coupled together to form a fuel cell stack.
A hydrogen-producing fuel cell system is a system that includes a hydrogen-producing processing assembly that is adapted to produce hydrogen gas and a fuel cell stack that is adapted to receive hydrogen gas produced by the fuel processing assembly and to generate an electric current therefrom. When the flow rate of hydrogen gas to the fuel cell stack is affected by the flow rate of feedstock(s) to the hydrogen-producing region of the hydrogen-generation assembly, this may affect the performance of the fuel cell stack and/or its ability to satisfy an applied load thereto.
In many fuel processing assemblies, the feed stream for the hydrogen-producing region is a liquid feed stream. The liquid feed stream is drawn from a suitable source or reservoir by a pump, and thereafter delivered to the hydrogen-producing region, typically after vaporizing the feed stream. In many such fuel processing assemblies, the liquid feed stream includes at least one of water and a carbon-containing feedstock, such as an alcohol or hydrocarbon. The rate at which the feed stream is pumped from the source to the hydrogen-producing region is typically related to the demand for hydrogen gas, with a greater flow rate of the feed stream provided when there is a greater demand for hydrogen gas produced by the fuel processing assembly, and a lesser flow rate when there is a lower demand. Reliable provision of the desired flow rate of the feed stream within a range of flow rates is a design goal for a fuel processing assembly, as the flow rate of feed stream affects the overall performance and/or operating conditions of the fuel processing assembly, and any hydrogen-producing fuel cell system of which the fuel processing assembly forms a portion thereof.